Short-wavelength laser module and method of producing the same

ABSTRACT

In a short-wavelength laser module, long-term reliability is lost because of unnecessary gas deposited on the end face of its optical waveguide. A short-wavelength laser module has a package structure wherein a package lid used when the short-wavelength laser module is hermetically sealed does not make contact with internal gas, and a process of accelerating the polymerization of a securing agent used inside the package is incorporated, whereby unnecessary gas from the securing agent is eliminated and the long-term reliability of the output is attained.

This application is a divisional of U.S. patent application Ser. No.10/220,100, filed Dec. 4, 2002, now U.S. Pat. No. 6,847,660, issued Jan.25, 2005, which is a U.S. National Phase Application of PCTInternational Application PCT/JP2001/11525, filed Dec. 27, 2001.

TECHNICAL FIELD

The present invention relates to a short-wavelength laser module havinga semiconductor laser housed in a package and outputtingshort-wavelength laser light and to a method of producing the lasermodule.

BACKGROUND OF TECHNOLOGY

In the optical device field, the hermetic sealing structure and hermeticsealing method of each optical device are important technologies toattain the long-term reliability of the optical device, and also in anoptical waveguide wavelength conversion device, the hermetic sealingstructure has become a very important factor, since it is necessary toprotect against external humidity and dust for stabilization of thecharacteristic of an optical waveguide itself, stabilization of thecharacteristic of an optical semiconductor, such as a semiconductorlaser, and attainment of long-term reliability.

In a hermetic sealing method in a conventional optical device, when ametallic package or a ceramic package is used in general, seam welding,such as resistance welding, can be applied between the main body of thepackage and the lid. For example, in the hermetic sealing method of anoptical semiconductor module, as disclosed in Japanese Laid-open PatentApplication No. Hei 6-82660, the module is configured so as to behermetically sealed by seam-welding or soldering the upper face of themain body and the lid. By this seam-welding and soldering, sufficienthermeticity can be maintained inside the package. However, when it isconsidered that a light-emitting device, such as a semiconductor laser,is mounted on an optical pickup, it is important to reduce the weightand cost of the package itself; since the package formed of a resin,such as plastic, is lightweight and inexpensive, the resin is one ofpromising package materials. In the case when a resin package is used, apackage sealing method using an adhesive, instead of the seam-welding orsoldering, is most effective.

In the case when an adhesive is used for a method of sealing a packageincluding a semiconductor laser and an optical waveguide wavelengthconversion device that makes the wavelength of the light of thesemiconductor laser short, in a conventional hermetically-sealingstructure shown in FIG. 13, a lid portion securing agent 1302 on theA-face 1308 of FIG. 13 makes contact with gas hermetically sealed insidethe package, whereby unnecessary gas 1306 evolved from the adhesive orunnecessary gas 1306 generated from the adhesive at the time of curingis mixed inside the package. In addition, an adhesive is used to securean optical waveguide wavelength conversion device 1304 and a sub-mount1305 inside the package, whereby unnecessary gas 1307 from the adhesiveis also mixed inside the package just as in the case of securing thelid.

Conventionally, in the case of an incoherent incandescent lamp, alight-emitting diode, a long-wavelength semiconductor laser or the like,large energy is not concentrated near its light-emitting point, wherebythe light-emitting point is not affected adversely. However,short-wavelength light emitted from a short-wavelength semiconductorlaser, such as a blue laser, or an optical waveguide, is coherent light,and large energy of 10 kW/cm² or more is concentrated near the end faceof the laser chip or the light-emitting point of the optical waveguide;therefore, the particles of the unnecessary gas are attracted thereto,and the unnecessary gas present inside the package are deposited on theend face of the chip or the end face of the optical waveguide, that is,the light emission portions, thereby causing the problem of lowering theoptical output.

In addition, in the case when an ultraviolet curing resin is used as apackage sealing and securing agent and an optical waveguide wavelengthconversion device securing agent, bluish violet light or ultravioletlight emitted from the semiconductor laser or the optical waveguidereacts with outside gas, that is, unnecessary caused by the ultravioletcuring resin present in the atmosphere inside the package, and theunnecessary gas is further deposited significantly on the end face ofthe optical waveguide, thereby causing the problem of losing long-termreliability.

Furthermore, in the case when the optical waveguide wavelengthconversion device is turned on continuously in the air atmospherewithout being secured to the inside of the package, large energy isconcentrated to the end face of the optical waveguide; therefore,foreign particles, such as dust, dirt and carbide, present in the air,are deposited on the end face of the blue light emission portion,thereby causing the problem of lowering the output of the blue light,deteriorating the transverse mode and losing the long-term reliability.

DISCLOSURE OF THE INVENTION

In order to solve the above-mentioned problems, the present invention isintended to provide a short-wavelength laser module capable of easingthe lowering of performance due to an adhesive used during production,attaining output stability and having long-term reliability, and toprovide a method of producing the laser module.

To achieve the above object, one aspect of the present invention is ashort-wavelength laser module comprising:

a light-emitting device including at least a semiconductor laser andoutputting short-wavelength laser light,

a package body having a disposition face on which said light-emittingdevice is disposed and a wall face surrounding said disposition face,

a lid portion joined to said package body, whereby a portion thereof,together with said disposition face and said wall face, forms housingspace in which said light-emitting device is housed, and

an adhesive used to bond said package body to said lid portion, wherein

said package is joined to said lid portion so as to have a sealing facewherein they make close contact and are aligned with each other, and

said sealing face is provided between said adhesive and said housingspace.

Another aspect of the present invention is the short-wavelength lasermodule, wherein the wavelength of the short-wavelength laser lightobtained by said light-emitting device is 450 nm or less.

Still another aspect of the present invention is the short-wavelengthlaser module, wherein said light-emitting device has wavelengthconverting means of converting the wavelength of the light output fromsaid semiconductor laser into a length of 450 nm or less.

Yet still another aspect of the present invention is theshort-wavelength laser module, wherein said semiconductor laser is ashort-wavelength semiconductor laser outputting light having awavelength of 450 nm or less.

Still yet another aspect of the present invention is theshort-wavelength laser module, wherein

at least portions, secured by said adhesive, of said lid portion havetranslucency, and

said adhesive is cured by the irradiation of ultraviolet light.

A further aspect of the present invention is the short-wavelength lasermodule, wherein inert gas is sealed in said housing space.

A still further aspect of the present invention is the short-wavelengthlaser module, wherein said housing space is in a state of vacuum.

A yet further aspect of the present invention is the short-wavelengthlaser module, wherein said package body and/or said lid portion have atranslucent light emission window.

A still yet further aspect of the present invention is theshort-wavelength laser module, wherein said adhesive is provided atleast at the joint portion between said package body and said lidportion, exposed to the outside of said short-wavelength laser module.

An additional aspect of the present invention is a method of producing ashort-wavelength laser module comprising:

a first securing step of securing a light-emitting device including atleast a semiconductor laser on a sub-mount using an adhesive that iscured by the irradiation of ultraviolet light,

a second securing step of securing said sub-mount, on which saidlight-emitting device is secured, inside a package using an adhesivethat is cured by heating,

an ultraviolet irradiation step of irradiating ultraviolet light toaccelerate the polymerization of said adhesive that is cured by theirradiation of said ultraviolet light, and

a sealing step of sealing said package to hermetically seal the insideof said package.

A still additional aspect of the present invention is the method ofproducing a short-wavelength laser module, further comprising a heatingstep of carrying out additional heating concurrently with or after saidultraviolet irradiation step to accelerate the polymerization of saidadhesive that is cured by said heating.

A yet additional aspect of the present invention is the method ofproducing a short-wavelength laser module, wherein the temperature atsaid heating step is higher than the temperature at said second securingstep and lower than the operation temperature of said short-wavelengthlaser module.

A still yet additional aspect of the present invention is acommunication apparatus having at least transmitting means oftransmitting information in the form of light, wherein

said transmitting means has the short-wavelength laser module.

In the present invention described above, for example, in theshort-wavelength laser module comprising a semiconductor laser and anoptical waveguide wavelength conversion device that halves thewavelength of its light, unnecessary gas generated from a package lidsecuring agent, an optical waveguide wavelength conversion devicesecuring agent and a sub-mount securing agent used at the time ofsealing is not affected by semiconductor laser light and harmonic light,whereby the long-term reliability of the output is attained duringlong-term continuous lighting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the configuration of the SHG blue light sourceof this embodiment;

FIG. 2( a) is a sectional view showing a structure of the package ofEmbodiment 1;

FIG. 2( b) is a perspective view showing the structure of the package ofEmbodiment 1;

FIG. 3 is a sectional view showing a structure of the package ofEmbodiment 1;

FIGS. 4( a) and 4(b) are sectional views showing structures of thepackage of Embodiment 1;

FIG. 5 is a graph showing a long-term reliability evaluationcharacteristic in Embodiment 1;

FIG. 6 is a sectional view showing a structure of the package ofEmbodiment 2;

FIG. 7 is a graph showing a long-term reliability evaluationcharacteristic in Embodiment 2;

FIG. 8 is a view showing the configuration of a GaN semiconductor laserof this embodiment;

FIG. 9 is a production process chart for an SHG blue light source inEmbodiment 4;

FIG. 10 is a graph showing an adhesion strength characteristic in a heatcycle test;

FIG. 11 is a graph showing a long-term reliability evaluationcharacteristic in Embodiment 4;

FIG. 12 is a graph showing a long-term reliability evaluationcharacteristic in Embodiment 4; and

FIG. 13 is a sectional view showing the structure of the conventionalpackage.

EXPLANATION OF REFERENCE CODES

11 x-plate MgO-doped LiNbO₃ substrate

12 optical waveguide QPM-SHG device

13 variable wavelength semiconductor laser

14, 83 Si sub-mount

15 proton-exchange optical waveguide

16 periodic polarization inversion domain

31, 41, 1301 metallic package lid

32, 42, 202 adhesive

33, 43, 1303 metallic package body

34, 44, 205 cover glass piece

35, 45 close-contact portion

36, 46, 213 outer peripheral contact area

81 semiconductor laser

82 reflection face

201 lid portion

203 main body portion

204, 604, 1306 unnecessary gas

206 inner face of lid portion

210 outer fringe portion

211, B-face

212, 612 C-face

601 lid portion

602 ultraviolet curing agent

610 ultraviolet light

611 ultraviolet light irradiator

1302 lid portion securing agent

1304 optical waveguide wavelength conversion

1305 sub-mount

1307 unnecessary gas in package

1308 A-face

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments in accordance with the present invention will be describedbelow referring to the drawings.

Embodiment 1

In Embodiment 1 of the present invention, an SHG blue light source isexplained wherein an optical-waveguide Quasi-Phase-MatchedSecond-Harmonic-Generation (hereafter referred to as QPM-SHG) deviceproduced on a MgO-doped LiNbO₃ substrate is used as an opticalwavelength conversion device, and a variable wavelength semiconductorlaser having a variable wavelength function is used as a semiconductorlaser. In this embodiment, when the semiconductor laser and the opticalwaveguide wavelength conversion device that halves the wavelength of itslight are hermetically sealed, a package structure wherein a lidsecuring agent is shut off from the inside of the package by aclose-contact portion is used to attain the long-term reliability of theoutput during long-term continuous lighting.

FIG. 1 is a view showing the configuration of the SHG blue light sourceof this embodiment. The SHG blue light source corresponding to thelight-emitting device of the present invention comprises an opticalwaveguide QPM-SHG device 12 and a variable wavelength semiconductorlaser 13 corresponding to the semiconductor laser of the presentinvention, mounted on a Si sub-mount 14. The optical waveguide QPM-SHGdevice 12 comprises a proton-exchange optical waveguide 15 and aperiodic polarization inversion domain 16 formed on an x-plate MgO-dopedLiNbO₃ substrate 11. The periodic polarization inversion domain 16 isproduced by forming a comb-shaped electrode on the +x face of theMgO:LiNbO₃ substrate and by applying an electric field. The differencebetween the propagation speed of the fundamental wave light and that ofthe second harmonic wave light is compensated for by the periodicpolarization inversion domain 16, thereby satisfying a quasi-phasematching condition. Since the fundamental and harmonic waves propagateas waveguide light inside the proton-exchange optical waveguide 15, along interaction length can be obtained, and high conversion efficiencycan be attained.

Next, a hermetically sealing structure using the package of the SHG bluelight source of this embodiment will be described. First, the variablewavelength semiconductor laser 13 is mounted accurately on the Sisub-mount 14 by soldering, and then the optical waveguide QPM-SHG device12 is mounted accurately with respect to the variable wavelengthsemiconductor laser 13 by using an ultraviolet curing resin. Then, theSi sub-mount 14 is secured at the desired position on the main body ofthe package by using a thermosetting epoxy adhesive.

Next, the configuration of the package in which the SHG blue lightsource is housed will be described. FIG. 2( b) is a perspective viewshowing only the package, and FIG. 2( a) is a sectional view taken online A-A′ of FIG. 2( b). However, FIG. 2( a) also shows thecross-section of the SHG blue light source housed in the package.

As shown in FIGS. 2( a) and (b), the package comprises a main bodyportion 203 corresponding to the main body portion of the package of thepresent invention and a lid portion 201 corresponding to the lid portionof the present invention; the outer fringe portion 210 of the hollow inthe main body portion 203, in which the SHG blue light source is housed,has a shape substantially identical to that of a C-face 212, that is,one of the faces of the inner face 206, having an L-shaped step incross-section, of the lid portion 201, and the outer fringe portion 210is positioned so as to be opposed to the C-face 212. The hollow in whichthe SHG blue light source is housed corresponds to the disposition faceand wall face of the present invention. On the other hand, a B-face 211,that is, the other portion of the inner face 206 of the lid portion thatis perpendicular to the C-face 212 and the other portion of the innerface 206 of the lid portion, is positioned so as to be opposed to theinner wall of the main body portion 203.

The lid portion 201 is joined to the main body portion 203 in which theSHG blue light source is housed so that the outer fringe portion 210mates with the C-face 212. At this time, the B-face 211 of the lidportion 201 makes close contact with the inner wall of the main bodyportion 203, whereby the hollow inside the main body portion 203, inwhich the SHG blue light source is disposed, and the face, exposed tothe space in which the SHG blue light source is disposed, of the lidportion 201 form a space in which the SHG blue light source is housed.This housing space corresponds to the housing space of the presentinvention.

An adhesive 202 for bonding and securing the main body portion 203 tothe lid portion 201 is applied between the outer fringe portion 210 andthe C-face 212; since the B-face 211 of the lid portion 201 makes closecontact with the inner wall of the main body portion 203, the sealingface of the present invention is formed between the housing space andthe adhesive 202; because of this sealing face, the adhesive 202 doesnot make contact with the atmosphere inside the housing space.

At this time, it is desirable that production is carried out so that theallowance of the distance from the B-face 211 to the B-face 211 on theside opposed thereto is +0.05 mm for the distance from the inner wall ofthe main body portion 203 to the inner wall on the side opposed thereto.Hence, at the sealing face, the close contact at the sealing facebetween the B-face 211 of the lid portion 201 and the inner wall of themain body portion 203 is enhanced at the time of hermetic sealing, andthe adhesive 202 is sufficiently shut off from the atmosphere in theinside space of the package.

On the other hand, a cover glass piece 205 is secured to the emissionface of the main body of the package by fusion bonding in advance, andthe Si sub-mount 14 is secured in a direction wherein the blue lightgenerated from the SHG blue light source is emitted perpendicularly withrespect to the face of the cover glass piece 205.

Next, the assembly of the package described above will be explained. Thelid portion 201 and the main body portion 203 in which the SHG bluelight source is disposed are placed in an atmosphere sufficiently filledwith N₂, and a state wherein the hollow of the main body 203 in whichthe SHG blue light source is disposed is sufficiently filled with N₂ ismaintained. The lid portion 201 is then fitted in the main body portion203; in a state wherein a sealing face is formed, the adhesive 204 isapplied between the C-face 212 of the lid portion 201 and the outerfringe portion 210 of the main body portion 203, thereby bonding andsecuring the lid portion 201 to the main body portion 203. At this time,as an example of the adhesive 202, a two-component epoxy adhesive isapplied to one or both of the C-face 212 and the outer fringe portion210.

After the bonding is completed, pressure is applied. Then, the packageis left for a certain period at room temperature, for example 24 hours,whereby the adhesive 204 is cured, and sufficient hermetic sealing isattained. The application of the adhesive 204 may be carried out beforethe lid portion 201 is fitted in the main body portion 203.

As an example of the lid portion 201, metal is used. In the packagestructure of the conventional example (FIG. 13), when a two-componentepoxy adhesive was used to hermetically seal the SHG blue light source,the output reduction in the fundamental wave light and the blue lightcaused by the deposition of foreign particles on the end face of theoptical waveguide was recognized after the continuous lighting of 5 mWblue light as shown in the graph of FIG. 5 because of unnecessary gaspresent inside the package; however, by using such a package structureas described in this embodiment, the deposition of foreign particles onthe end face is not recognized after the continuous lighting of the 5 mWblue light, whereby long-term reliability for 1000 hours is attained.

As described above, in this embodiment, the lid portion 201 is providedwith the B-face 211 and the C-face 212 so as to have an L-shapedstructure; hence, it is possible to prevent the uncured portion of theadhesive or the cured adhesive from entering the inside of the packagein which the SHG blue light source is disposed and from mixing in theatmosphere thereof. For this reason, unnecessary gas 204 is notdeposited on the emission end face of the SHG blue light source, and theoutput reduction of the laser light does not occur.

In this embodiment, the deposition of foreign particles on the end faceis prevented during the continuous lighting of the laser, wherebylong-term reliability is attained, and its practical effect issignificant.

Furthermore, in this embodiment, metal is used for the lid portion 201;however, even when glass or a resin material such as plastic is used, asimilar sealing method can be attained, and it is preferable that thelid becomes more light-weight and inexpensive. Moreover, the adhesive isnot limited to a two-component epoxy adhesive; a one-componentthermosetting adhesive, a one-component cold setting adhesive, etc. mayalso be used.

In addition, the adhesive 202 may be applied to the whole outsideperipheral contact area between the main body portion 203 and the lidportion 201. In this state, when viewed externally, the joint linebetween the main body portion 203 and the lid portion 201 is covered bythe adhesive. This case is superior to the case wherein the adhesive isapplied to some portions of the outside peripheral contact area withrespect to reliability at the time of a heat cycle test or with respectto reliability against impact or the like, whereby its practical effectis significant.

Furthermore, in the above explanations, N₂ gas was used when the housingspace was hermetically sealed; however, a different kind of gas, such asrare gas, may also be used, provided that the gas is inert gas.Furthermore, the inside of the housing space may be made vacuum withoutusing gas. In this case, the intensity of the close contact at thesealing face is enhanced owing to the difference between the pressureinside the housing space and the pressure of the air at the package lidportion, whereby hermetic sealing is enhanced, making the mixture entryof the adhesive into the package difficult, and the effect of thepresent invention can thus be improved further.

Still further, the structure of the package is not limited to theconfiguration, having the L-shaped step in cross-section, of the lidportion 201; as shown in FIG. 3, a close contact face 35 wherein a mainbody portion 33 makes close contact with a lid portion 31 may also beformed to have a taper shape so as to be oblique with the inside wall ofthe main body portion 33. At this time, a lid portion securing agent 32is applied so as to seal the joint line between the main body portion 33and the lid portion 31, exposed at the lid portion.

In the case of the configuration shown in FIG. 3, the whole of the closecontact face 35 forms the sealing face of the present invention; wherebythe lid portion securing agent 32 can be shut off from the inside of thepackage, and the uncured portion of the lid portion securing agent 32 orunnecessary gas generated during curing does not enter the housing spaceinside the package. Furthermore, because of the taper shape, byincreasing the amount of pressure application from the upper face of thelid portion 31, the close contact can be enhanced further in comparisonwith the structure shown in FIG. 2, thereby being more effective.Moreover, by securing the lid portion 31 while applying pressure, theshut-off of the close contact face 35 from the outside can be enhancedfurther, thereby being effective.

In addition, in the structure of the lid portion, even when the contactfaces of a lid portion 41 and a main body portion 43 are made to have anL-shaped step structure as shown in FIGS. 4( a) and (b), a close contactportion 45 formed by the joining and close contact between the lidportion 41 and the main body portion 43 becomes a sealing face, and alid portion securing agent 42 can be shut off from the inside of thepackage, whereby unnecessary gas generated from the lid portion securingagent 42 does not enter the inside of the package. In this case, byincreasing the amount of pressure application just as in the case of thestructure shown in FIG. 3, the close contact at the close contactportion can be enhanced further. Furthermore, this structure can beproduced more easily than the structure of FIG. 3, thereby being moreeffective. In particular, in FIG. 4( a), a groove 450 is formed at thefringe portion of the lid portion 41, to which the lid portion securingagent 42 is applied, whereby the lid portion securing agent 42 can beapplied more easily, thereby being more effective.

In addition, in this embodiment, the external shape of the package is arectangular shape; however, the external shape of the package is notlimited to a rectangular shape; a cubic shape, a polygonal shape, asemi-cylindrical shape, etc. may also be used. As the internal shape ofthe package, it is important to provide a securing portion between themain body portion and the lid portion by using the adhesive on theoutside of the sealing portion wherein the main body portion makes closecontact with the lid portion to prevent the outside gas of the securingagent from entering the inside of the package.

In short, in the present invention, the sealing face wherein the lidportion makes close contact with the main body of the housing shouldonly be formed between the housing space formed by the lid portion andthe main body of the housing and the adhesive used to bond the lidportion to the main body of the housing; hence, the sealing face is notlimited by the outside shapes of the main body of the housing and thelid portion, the actual shape of the hollow of the main body in whichthe optical device is disposed, the actual configuration of the sealingface, the application position, the filling position of the adhesive,etc., or the like.

Embodiment 2

In this embodiment, when the semiconductor laser, the optical waveguidewavelength conversion device that halves the wavelength of its light andthe Si sub-mount are hermetically sealed, an ultraviolet curing agenthaving intense reactivity in a short-wavelength range is used as apackage lid securing agent. As a result, the long-term reliability ofthe output is attained during long-term continuous lighting, just as inthe case of Embodiment 1.

A hermetically sealing structure using the package of the SHG blue lightsource of this embodiment will be described using FIG. 6. In the figure,the portions identical or corresponding to those shown in FIG. 2 aredesignated by the same reference codes, and their detailed explanationsare omitted. In addition, a lid portion 601 is different in that it ismade of a transparent material, such as a glass plate. Furthermore, evenin this embodiment, just as in the case of Embodiment 1, an SHG bluelight source is taken as an example, wherein an optical-waveguideQPM-SHG device produced on a Mgo-doped LiNbO₃ substrate is used as anoptical wavelength conversion device, and a variable wavelengthsemiconductor laser having a variable wavelength function is used as asemiconductor laser.

Next, the assembly method of the package of this embodiment will bedescribed using FIG. 6. Just as in the case of Embodiment 1, theoptical-waveguide QPM-SHG device and the variable wavelengthsemiconductor laser mounted on the Si sub-mount are secured at thedesired position on the main body of the package by using athermosetting epoxy adhesive or the like.

Next, the main body of the package is placed in an atmospheresufficiently filled with N₂ gas, and a state wherein the inside of themain body of the package in which the SHG blue light source is disposedis sufficiently filled with N₂ gas is maintained. The lid portion 601 isthen fitted in the main body 203; in a state wherein a sealing face isformed, an ultraviolet curing agent 602 is applied between the C-face612 of the lid portion 601 and the outer fringe portion 210 of the mainbody portion 203, the lid portion 601 is bonded to the main body 203,and pressure is applied. Furthermore, concurrently with the pressureapplication, ultraviolet light 610 is applied from an ultraviolet lightirradiator 611 to the lid portion 601 of the package; the application iscarried out centrally at each of two left and right positions for about60 seconds to cure the ultraviolet curing agent 602, whereby the lidportion 601 is bonded and secured to the main body portion 203, and theinside of the main body portion of the package is hermetically sealed.

Since the configurations of the lid portion 601 and the main body 203are similar to those of Embodiment 1, it is possible to prevent theuncured portion of the ultraviolet curing agent or the cured adhesivefrom entering the inside of the package in which the SHG blue lightsource is disposed and from mixing in the atmosphere inside the package.For this reason, unnecessary gas 604 is not deposited on the emissionend face of the SHG blue light source, and the output reduction of thelaser light does not occur.

In the case when the ultraviolet curing agent is used to hermeticallyseal a semiconductor laser of a wavelength of 450 nm or less, anothervisible light laser and an optical waveguide wavelength conversiondevice, the wavelength of the emitted light is not in a wavelength rangewherein reaction with the ultraviolet curing agent occurs. However, whena light source of a short wavelength range of 450 nm or less ishermetically sealed just as in the case of this embodiment, thereactivity of the ultraviolet curing agent is enhanced as the wavelengthbecomes shorter. Hence, as clearly shown in FIG. 7, in the conventionalpackage structure (FIG. 13), when the ultraviolet curing agent was usedto hermetically seal the blue SHG light source, after the continuouslighting of the blue light, the output reduction of the fundamental wavelight and the blue light due to the deposition of foreign particles onthe end face of the optical waveguide was recognized.

By using such a package structure as used in this embodiment, thedeposition of foreign particles on the end face after the continuouslighting of blue light having an output of 5 mW was not recognized,whereby the long-term reliability of the semiconductor laser light andthe blue light for 1000 hours was attained as shown in FIG. 7.

In this embodiment, the ultraviolet curing agent is used as a packagelid securing agent; even in a short wavelength range of 450 nm or lesswherein the reactivity with the ultraviolet curing agent is high, thedeposition of foreign particles on the end face is prevented, wherebythe long-term reliability of the wavelength-converted blue light isattained, and its practical effect is significant. In addition, incomparison with the adhesives, such as the two-component epoxy adhesiveand the thermosetting adhesive of Embodiment 1, the ultraviolet curingagent has a very short curing time; hence, in the mass production of theshort-wavelength laser modules, production time can be shortened,whereby its practical effect is significant.

In this embodiment, the package having the structure of FIG. 2 inEmbodiment 1 was used as the package; however, the package lids havingstructures shown in FIGS. 3 and 4 may be used, and hermetic sealing maybe carried out while pressure is applied. In this case, the shut-offperformance between the ultraviolet curing agent and the inside of thepackage is enhanced, whereby its practical effect is significant.

In addition, in this embodiment, a glass material is used for the lidportion 601; however, a resin material, such as plastic, may also bepreferably used, provided that the material is transparent or somewhattranslucent, for example 30% or more, in the wavelength range of theirradiator of the ultraviolet curing agent, since a similar sealingmethod can be used and its weight is made lighter.

Furthermore, in this embodiment, it was explained that the whole of thelid portion 601 is translucent; however, some portions of the lidportion of the present invention wherein the ultraviolet curing agent isirradiated should only be translucent.

Still further, in the above-mentioned Embodiment 2, the SHG blue lightsource was used; however, a GaN semiconductor laser of a wavelength of410 nm may also be used instead of the SHG blue light source, as theoptical device of the present invention. As shown in FIG. 8, a GaNsemiconductor laser 81 is mounted so as to be secured to a Si sub-mount83 by soldering for example. The sub-mount 83 can be disposed just as inthe case of Embodiment 2; as shown in FIG. 8, the light emitted from theGaN semiconductor laser 81 is reflected by a reflection face 82,delivered upward, and output from the transparent lid portion 601 to thelid portion.

The GaN semiconductor laser of a wavelength of 410 nm was hermeticallysealed in each of the conventional package and the package of thepresent invention, and a long-term reliability test was carried out. Asa result, in the case of the conventional package, the output reductionof light due to the deposition of foreign particles on the end face ofthe semiconductor chip was caused, just as in the case of the SHG bluelight source; however, in the case of the package of this embodiment,the deposition of foreign particles on the end face of the semiconductorchip was not recognized, and the long-term reliability of the laser for1000 hours was attained.

As described above, although the GaN semiconductor laser 81 outputsviolet light, by using the GaN semiconductor laser in the configurationof the above-mentioned embodiment, the long-term reliability of theoutput can be attained during the long-term continuous lighting of theviolet light.

Although it was mentioned that the wavelength of the GaN semiconductorlaser was 410 nm, the wavelength may be different. In addition, theshape of the Si sub-mount is not required to be limited to that shown inFIG. 8, but the shape shown in FIG. 1 may also be used. In this case,the GaN semiconductor laser can be housed and used in the package havingthe configuration of Embodiment 1.

Embodiment 3

In this embodiment, by introducing a process of accelerating thepolymerization of the securing agent that is used when the opticalwaveguide wavelength conversion device is secured to the Si sub-mount,the long-term reliability of the output is attained during the long-termcontinuous lighting of high-output blue light subjected to wavelengthconversion. In this embodiment, just as in the case of Embodiment 1, itis explained that an SHG blue light source wherein an optical-waveguideQPM-SHG device produced on a MgO-doped LiNbO₃ substrate is used as anoptical waveguide wavelength conversion device, and a variablewavelength semiconductor laser having a variable wavelength function isused as a semiconductor laser is used, and the SHG blue light source ismounted on the main body portion 201 of Embodiment 1.

FIG. 9 shows a process of producing the SHG blue light source of thisembodiment. First, the variable wavelength semiconductor laser 13 ismounted accurately on the Si sub-mount 14 by soldering (at 911), andthen the optical waveguide QPM-SHG device 12 is mounted accurately withrespect to the variable wavelength semiconductor laser 13 by using anultraviolet curing resin (at 912). Then, the Si sub-mount 14 is securedat the desired position on the main body 203 by using a thermosettingepoxy adhesive (at 913). At this time, the cover glass piece 205 hasbeen secured to the emission face of the main body 203 by fusionbonding, and the Si sub-mount is secured so that the emitted blue lightis delivered perpendicularly with respect to the face including thecover glass piece 205.

Generally, the amount of unnecessary gas after the curing of theadhesive is less than that before the curing, and unnecessary gas isgenerated during the curing. Hence, the unnecessary gas generated fromthe ultraviolet curing resin used to secure the optical waveguideQPM-SHG device 12 and from the thermosetting epoxy adhesive used tosecure the Si sub-mount 14 before and during the curing can be purgedoutside the main body 201 in a state wherein the space in which the Sisub-mount 14 is disposed is not hermetically sealed. However, even afterthe curing, residual unnecessary gas is present in the adhesive; hence,even a very small amount of the unnecessary gas may adversely affect thelong-term reliability of the SHG blue light source after the completion.

In order to examine the influence of the residual unnecessary gas, byusing an epoxy ultraviolet curing adhesive generating a relatively smallamount of unnecessary gas to secure the SHG blue light source and byusing an epoxy thermosetting adhesive to secure the Si sub-mount 12, theunnecessary gas after the continuous lighting of the laser wasevaluated. At this time, an ultraviolet irradiation amount of about 3000mJ (corresponding to the manufacturer recommended value) was used forultraviolet curing, and as a method of curing the thermosetting resin,heat treatment was carried out at 60° C. for 1 hour in a constanttemperature bath. In addition, the shape of the package and the methodof the assembly thereof at the time of hermetic sealing are madeidentical to those of Embodiment 2.

EXAMPLE 1

First, when fundamental wave light (a wavelength range of 800 nm) wasemitted continuously and the end face was observed, the deposition offoreign particles on the end face was not recognized, and thereliability of the fundamental wave was attained by using an adhesivegenerating a scarce amount of unnecessary gas. However, even when theadhesive generating a scarce amount of unnecessary gas was used, whenthe end face was observed after high-output blue light (a wavelengthrange of 400 nm and an output of 10 mW) was emitted continuously, thedeposition of foreign particles was observed. It was presumed that thiswas caused by that the unnecessary gas from the adhesive remaininginside the package or the unnecessary gas generated from the uncuredadhesive was deposited on the end face of the device; it was thus foundthat even in the epoxy adhesive generating a scarce amount ofunnecessary gas, the existence of a small amount of unnecessary gasadversely affected the long-term reliability.

In addition, even after the curing of the adhesive, it was presumed thatin the progress state of photo polymerization, the adhesive generatedunnecessary gas during the photo polymerization, and the generated gasalso caused adverse effect in this experiment. FIG. 10 shows an adhesionstrength characteristic in a heat cycle test ranging from −40 to 85° C.,and it is recognized that the adhesion strength increases in the rangefrom 0 to 100 cycles. This is presumed that the polymerization of theadhesive was accelerated and the adhesion strength increased during theheat cycle test.

Furthermore, the absorption end of the SHG device (MgO-doped LiNbO₃substrate) used as an adherent is 320 nm; a wavelength of 320 nm or lessdoes not pass through when ultraviolet light is emitted to secure theSHG device using an ultraviolet curing agent. On the other hand, thecuring wavelength of the ultraviolet curing agent varies depending onthe adhesive; however, the curing wavelength of each adhesive is notlimited to a single wavelength; an initiator is included so that curingoccurs at a plurality of specific wavelengths in the ultraviolet tovisible light ranges. However, in the case when a MgO-doped LiNbO₃substrate is used as an adherent, an initiator that carries outpolymerization at a wavelength of 320 nm or less cannot contribute tothe curing of the adhesive. In other words, since the ultraviolet curingagent must be cured completely by an initiator that carries outpolymerization at a wavelength of 320 nm or more, a sufficientirradiation amount of ultraviolet light is required. The ultravioletcuring agent used for this embodiment has an optimal curing wavelengthof about 330 nm. Since the transmission factor of the MgO-doped LiNbO₃substrate at a wavelength of 330 nm is about 50%, the integrated amountof the ultraviolet light applied to the ultraviolet curing agent isabout half the integrated amount of the light emitted from an actualirradiator.

On the basis of this, in order to accelerate the polymerization of theadhesive and to completely remove unnecessary gas, after the SHG bluelight source is secured, the additional application of ultraviolet lightis carried out at the manufacturer recommended irradiation amount ormore required for complete curing, that is, two times or more therecommended amount in this embodiment (6000 mJ or more, the manufacturerrecommended value: 3000 mJ), and an unnecessary gas countermeasure stepwherein heat treatment at 60° C. for 10 hours in a constant temperaturebath after the securing of the Si sub-mount 14 is incorporated (at 914of FIG. 9). The irradiation amount of the ultraviolet light at this timeis an irradiation amount sufficient for the complete curing of theadhesive in consideration of the ultraviolet light transmission factorof the SHG device, and the heat treatment is carried out at theoperation temperature (the operation temperature herein is roomtemperature of 25° C.) or more of the SHG blue light source, therebyeliminating the generation of unnecessary gas due to non-curing of theadhesive and the generation of unnecessary gas in the operationenvironment.

In addition, the influence of the optical waveguide portion on theoptical waveguide QPM-SHG device 12 owing to thermal diffusion in theheat treatment at 60° C. for 10 hours, that is, the change in therefraction factor of the optical waveguide portion, is negligibly small;hence, the optical waveguide characteristic, that is, the optical outputcharacteristic of the SHG blue light source depending on the reductionin the efficiency of the optical coupling to the optical waveguide doesnot change. As a result, as shown in FIG. 11, the deposition to the endface of the device was not recognized 500 hours after the continuouslighting of the blue light having an output of 10 mW, whereby thereduction of the output was eliminated, and the long-term reliability ofthe SHG blue light source at the time of high output is attained.

EXAMPLE 2

When the operating temperature and storage temperature of the SHG bluelight source rise, it is necessary to set a heat treatment temperatureso as to be higher than the operating temperature and storagetemperature in order to prevent the generation of unnecessary gas; inaddition, as the heat treatment process at that time, it is necessary toset a process wherein the influence due to thermal diffusion to theoptical waveguide portion can be neglected. When using the SHG bluelight source as an optical disc light source, it is necessary to use aheat treatment process of 85° C. or more, since the upper storagetemperature is generally 85° C. The heat treatment process to eliminateunnecessary gas was carried out at 100° C. for 10 hours. The diffusionamount d at the waveguide due to heat diffusion at this time can berepresented by d=2×[D(T)×t]^(1/2) (D: a diffusion constant and afunction of T, T: a heat treatment temperature, and t: a heat treatmenttime).

Usually, the heat treatment process at the time of producing aproton-exchange waveguide, such as the optical waveguide QPM-SHG device12, is carried out at T=330° C. for t=3 hours; the diffusion amount inthe case of the heat treatment process at T=100° C. for t=10 hours isless than that of the thermal diffusion in the case of the usualproduction of the proton-exchange waveguide by two orders of magnitudeor more, and the diffusion amount is very small to the extent that thediffusion amount does not adversely affect the optical waveguidecharacteristic. In other words, this process can be used as a processnot adversely affecting the optical waveguide characteristic and as aprocess of completely eliminating unnecessary gas. When the temperatureof the heat treatment process is in the range of T=100 to 200° C., theoptical waveguide characteristic is not adversely affected in the heattreatment process for about t=10 hours, and unnecessary gas can beeliminated, whereby a sufficient heat treatment process can be carriedout at the upper storage temperature of t=200° C. or less.

In this embodiment, the configuration shown in FIG. 4( a) was used asthe package, and a process of applying and curing the lid portionsecuring agent 42 while applying pressure to the lid portion 41 at thetime of hermetic sealing was incorporated. The hermetic sealing wascarried out by securing the lid portion 41 using the lid portionsecuring agent 42; however, it may be possible to use a hermetic sealingmethod wherein after the lid portion 41 is secured first using the lidportion securing agent 42, a cover glass piece 44, serving as a lightemission window, of the main body portion 43 is fusion-bonded andsecured in the end. In other words, even if unnecessary gas from the lidportion securing agent 42 used to secure the package lid is presentinside the package, by carrying out the heat treatment process beforethe fusion-bonding, the unnecessary gas can be purged to the outside ofthe package from the light emission window portion in which the coverglass piece 44 is not yet installed, whereby its practical effect issignificant.

In addition, the hermetic sealing was carried out by securing the lidportion 41 using the adhesive; however, as a package lid securingmethod, it may also possible to use a method wherein the entireperipheral portion of the lid portion, except for some portions, isfilled with the adhesive, and the unfilled portions are filled in theend so as to be secured. Hence, even if unnecessary gas from theadhesive used to secure the package lid is present inside the package,the unnecessary gas can be purged from the unfilled portions to theoutside of the package, whereby its practical effect is significant.

As described above, in this embodiment, by securing the opticalwaveguide QPM-SHG device 12 comprising the semiconductor laser and theoptical waveguide wavelength conversion device directly connected toeach other on the Si sub-mount to the inside of the hermetically sealedpackage, the end face of the SHG device is protected against dirt, dustand carbide present in the air atmosphere, whereby the long-termreliability of the output can be attained during the long-termcontinuous lighting of the high-output blue light subjected towavelength conversion. In the SHG blue light source using thesemiconductor laser and the optical wavelength conversion device,foreign particles present in the air are deposited on the emission endface during the continuous lighting, and the reduction of the output andthe deterioration in the transverse mode are caused. So it has been aserious problem.

When the directly-coupled short-wavelength laser module, nothermetically sealed inside the package shown in FIG. 1, was turned oncontinuously in a state wherein the emission end face made contact withthe air atmosphere without being hermetically sealed inside the package,foreign particles in the air were deposited on the emission end face,and as shown in FIG. 12, the output reduction of blue light and thedeterioration in the transverse mode were caused. Hence, by hermeticallysealing the short-wavelength laser module using the method of Embodiment4, it is possible to prevent the deposition of the foreign particles inthe air on the emission end and to prevent the deposition of outside gasgenerating from the securing agent described in Embodiment 4, wherebythe long-term reliability of the output and in the transverse mode canbe attained.

FIELD OF INDUSTRIAL APPLICATION

As described above, in accordance with the present invention, thereliability of the output during the long-term lighting of theshort-wavelength light can be attained.

Furthermore, by eliminating the unnecessary gas generating from thesecuring agent at the time of producing the short-wavelength lasermodule, it is possible to prevent the deposition of the foreignparticles on the emission end face of the optical device, whereby thelong-term reliability of the output during the high-output lighting ofblue light can be attained.

1. A method of producing a short-wavelength laser module, the methodcomprising: a first securing step of securing an optical wavelengthconversion device on a sub-mount using an adhesive that is cured byirradiation with ultraviolet light, a second securing step of securingsaid sub-mount, on which said optical wavelength conversion device issecured, inside a package using an adhesive that is cured by heating, anultraviolet irradiation step of irradiating ultraviolet light toaccelerate the polymerization of said adhesive that is cured by theirradiation with said ultraviolet light, a heating step of carrying outan additional heating concurrently with or after said ultravioletirradiation step to accelerate the polymerization of said adhesive thatis cured by said heating, and a sealing step of sealing said package tohermetically seal the inside of said package; wherein the sealing stepis carried out after the ultraviolet irradiation step and after theheating step; and wherein said package is sealed with a bonding adhesiveand said bonding adhesive does not make contact with the atmosphereinside said package.
 2. The method of producing a short-wavelength lasermodule in accordance with claim 1, wherein the temperature at saidheating step is higher than the temperature at said second securing stepand lower than the operation temperature of said short-wavelength lasermodule.
 3. The method of producing a short-wavelength laser module inaccordance with claim 1, wherein said package comprises a lid portionand a main body portion, said lid portion is a transparent material, andsaid lid portion is secured to said main body portion by said bondingadhesive that is cured by the irradiation with ultraviolet light.
 4. Themethod of producing a short-wavelength laser module in accordance withclaim 1, wherein: said package comprises a lid portion and a main bodyportion, said lid portion is a transparent material, and said lidportion is secured to said main body portion by said bonding adhesive.5. The method of producing a short-wavelength laser module in accordancewith claim 1, wherein said bonding adhesive is a two-component epoxyadhesive.
 6. The method of producing a short-wavelength laser module inaccordance with claim 1, wherein the optical wavelength conversiondevice comprises an optical-waveguide quasi-phase-matchedsecond-harmonic-generation device.